WAIT 1.8
Copyright (c) 1996-2000, Ulrich Pfeifer
------------------------------------------------------------------------
This program is free software; you can redistribute it and/or
modify it under the same terms than Perl itself.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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News:
Locking
=======
WAIT now supports some basic locking.
Speed
=====
Searching large collections is now considerably faster:
$table->search({attr => 'text',
cont => $query,
top => 1,
picky => 0});
Table indices may now be tuned to improve search performance. The
index tuning can be switched on and off using $table->set(top=>1/0) to
allow for bulk inserts.
Documentation
=============
WAIT is still not documented really. But Andreas König took the
trouble to comment the example scripts. This will help you
implementing your own applications. I added some tiny scripts to
index e.g. your .yow file or the fourtune databases.
SourceForge
===========
WAIT is registered on SourceForge now:
http://wait.sourceforge.net/
https://sourceforge.net/project/?group_id=4814
I will keep the CVS repository up to date. If you have some spare
tuits, feel free to contribute.
Ulrich Pfeifer
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NAME
WAIT - a rewrite of the freeWAIS-sf engine in Perl and XS
SYNOPSIS
A Synopsis is not yet available.
Status of this document
I started writing down some information about the implementation before
I forget them in my spare time. The stuff is incomplete at least. Any
additions, corrections, ... welcome.
PURPOSE
As you might know, I developed and maintained freeWAIS-sf (with the help
of many people in The Net). FreeWAIS-sf is based on freeWAIS maintained
by the Clearing House for Network Information Retrieval (CNIDR) which in
turn is based on wais-8-b5 implemented by Thinking Machine et al. During
this long history - implementation started about 1989 - many people
contributed to the distribution and added features not foreseen by the
original design. While the system fulfills its task now, the code has
reached a state where adding new features is nearly impossible and even
fixing longstanding bugs and removing limitations has become a very time
consuming task.
Therefore I decided to pass the maintenance to WSC Inc. and built a new
system from scratch. For obvious reasons I choosed Perl as
implementation language.
DESCRIPTION
The central idea of the system is to provide a framework and the
building blocks for any indexing and search system the users might want
to build. Obviously the framework limits the class of system which can
be build.
+------+ +-----+ +------+
==> |Access| ==> |Parse| ==> | |
+------+ +-----+ | |
|| | | +-----+
|| |Filter| ==> |Index|
\/ | | +-----+
+-------+ +-----+ | |
<= |Display| <== |Query| | |
+-------+ +-----+ +------+
A collection (aka table) is defined by the instances of the access and
parse module together with the filter definitions. At query time in
addition a query and a display module must be choosen.
Access
The access module defines which documents are members of a database.
Usually an access module is a tied hash, whose keys are the Ids of the
documents (did = document id) and whose values are the documents
themselves. The indexing process loops over the keys using `FIRSTKEY'
and `NEXTKEY'. Documents are retrieved with `FETCH'.
By convention access modules should be members of the `WAIT::Document'
hierarchy. Have a look at the `WAIT::Document::Split' module to get the
idea.
Parse
The task of the parse module is to split the documents into logical
parts via the `split' method. E.g. the `WAIT::Parse::Nroff' splits
manuals piped through nroff(1) into the sections *name*, *synopsis*,
*options*, *description*, *author*, *example*, *bugs*, *text*, *see*,
and *environment*. Here is the implementation of `WAIT::Parse::Base'
which handles documents with a pretty simple tagged format:
AU: Pfeifer, U.; Fuhr, N.; Huynh, T.
TI: Searching Structured Documents with the Enhanced Retrieval
Functionality of freeWAIS-sf and SFgate
ER: D. Kroemker
BT: Computer Networks and ISDN Systems; Proceedings of the third
International World-Wide Web Conference
PN: Elsevier
PA: Amsterdam - Lausanne - New York - Oxford - Shannon - Tokyo
PP: 1027-1036
PY: 1995
sub split { # called as method
my %result;
my $fld;
for (split /\n/, $_[1]) {
if (s/^(\S+):\s*//) {
$fld = lc $1;
}
$result{$fld} .= $_ if defined $fld;
}
return \%result;
}
Since the original document cannot be reconstructed from its attributes,
we need a second method (*tag*) which marks the regions of the document
with tags for the different attributes. This tagged form is used by the
display module to hilight search terms in the documents. Besides the
tags for the attributes, the method might assign the special tags `_b'
and `_i' for indicating bold and italic regions.
sub tag {
my @result;
my $tag;
for (split /\n/, $_[1]) {
next if /^\w\w:\s*$/;
if (s/^(\S+)://) {
push @result, {_b => 1}, "$1:";
$tag = lc $1;
}
if (defined $tag) {
push @result, {$tag => 1}, "$_\n";
} else {
push @result, {}, "$_\n";
}
}
return @result; # we don't go for speed
}
Obviously one could implement `split' via `tag'. The reason for having
two functions is speed. We need to call `split' for each document when
indexing a collection. Therefore speed is essential. On the other hand,
`tag' is called in order to display a single document and may be a
little slower. It may care about tagging bold and italic regions. See
`WAIT::Parse::Nroff' how this might decrease performance.
Filter definition
From the Information Retrieval perspective, the hardest part of the
system is the filter module. The database administrator defines for each
attribute, how the contents should be processed before it is stored in
the index. Usually the processing contains steps to restrict the
character set, case transformation, splitting to words and transforming
to word stems. In WAIT these steps are defined naturally as a pipeline
of processing steps. The pipelines are made up by functions in the
package WAIT::Filter which is pre-populated by the most common functions
but may be extended any time.
The equivalent for a typical freeWAIS-sf processing would be this
pipeline:
[ 'isotr', 'isolc', 'split2', 'stop', 'Stem']
The function `isotr' replaces unknown characters by blanks. `isolc'
transforms to lower case. `split2' splits into words and removes words
shorter than two characters. `stop' removes the freeWAIS-sf stopwords
and `Stem' applies the Porter algorithm for computing the stem of the
words.
The filter definition for a collection defines a set of pipelines for
the attributes and modifies the pipelines which should be used for
prefix and interval searches.
Several complete working examples come with WAIT in the script
directory. It is recommended to follow the pattern of the scripts
smakewhatis and sman.